1. Field of the Invention
This invention relates generally to an access device for a surgical procedure and, more particularly, to a minimally invasive access device for spinal surgery, where the device includes retractor blades and an access tube, where the access tube is threaded into the retractor blades to cause them to separate, which provides a corridor for accessing a surgical pathology.
2. Discussion of the Related Art
Traditional surgical approaches for the human body involve the dissection of supporting structures, such as muscle, ligaments and/or bone, to access and expose the pathology being treated. These structures are usually vital to the long term health and function of the body. Typically, these structures are not involved in a disease process, but frequently need to be removed or dissected in order to gain visualization of the pathology.
In the case of spinal disorders, the supporting muscle and ligaments of the spine are removed to expose the underlying bony part of the spine where the pathology is typically located. These supporting structures are not causing the patient any discomfort or pain, however, because the surgeon must be able to visualize the surgical operation, they need to be removed or detached. For example, in the treatment of a lumbar disk herniation or stenosis, the muscle and ligaments are dissected from the spine to expose the lamina of the spine, sometimes over many levels of the spine. In performing spinal fusion and instrumentation, extensive muscle and ligamentous detachment may be performed. As a result, these tissues never return to their normal anatomical position, which is disrupted in the surgical process, weakening their function and strength. Also, the patient may experience significant pain and discomfort resulting in longer hospital stays and recoveries. The long term health of the spine can also be affected because these supporting structures are not able to perform their function normally. This can result in further pain and discomfort, and can even lead to additional surgeries.
A frequently encountered problem is transitional syndrome whereby the nerves adjacent to an open fusion and instrumentation become compressed. The treatment is often an additional surgery with extension of the fusion and instrumentation. This may in-part be due to the initial fusion procedure dissecting supporting muscles and ligaments creating an iatrogenic instability that leads to adjacent level stenosis. In addition, large open procedures often result in extensive scar formation that can lead to conditions such as arachnoiditis and failed back syndrome. These patients suffer significant and debilitating pain which is often refractory to additional surgery. Many can no longer work or conduct normal activities of daily living.
In an attempt to preserve normal anatomical structures during spine surgery, minimally invasive surgical procedures have been devised. One such procedure involves the use of a series of muscle dilators that spread open the muscle fibers of the spine to create a pathway to the spine. A Kirschner (K) wire (a thin metal wire) is initially introduced through a small incision and directed towards the spinal pathology. The position of the K-wire is visualized by a fluoroscopic imaging system to identify its location. An initial narrow diameter muscle dilator is passed over the K-wire, and the K-wire is removed and subsequent larger muscle dilators are continually passed. When the opening is large enough, an access tube or retractor is positioned around the last muscle dilator through which the surgery is performed. The inner sequential muscle dilators are then removed allowing the surgeon to operate through the tubular retractor. The retractors come in a variety of lengths and diameters for different patients and procedures.
Unfortunately, a number of complications have occurred using the previously described system. The K-wire is very thin and sharp and can be easily passed to deep and into the spinal cord or injure a nerve root or large blood vessel. Additionally considerable downward force is required to pass the muscle dilators towards the spine. Incidences have occurred in which the dilators are passed into the spinal canal resulting in neural injury and paralysis. The muscle dilators also tend to be pushed upward out of the wound requiring multiple repositioning during placement, each time placing the neural structures at risk. This is especially true for large muscular individuals. Lastly, multiple, sequentially larger dilators are used causing considerable patient risk with placement of each muscle dilator. Therefore, it is desirable to improve the known minimally invasive surgical access devices.